99 Ford Escort P0455 and P0172 Codes: Vacuum Leak Diagnosis & EVAP System Issues
I'm a 22-year-old female with no prior car knowledge and am currently facing serious issues with my 1999 Ford Escort. I recently discovered two diagnostic trouble codes: P0455 and P0172, but can't find clear explanations online. The auto parts store suggested a vacuum leak as the likely cause. However, I've already spent $2000 at a previous mechanic who hasn as effectively resolved the problem. Can anyone explain what these codes mean in simple terms? Specifically: - P0455: Indicates a large evaporative system leak, often linked to EVAP system integrity. - P0172: Shows the engine is running too rich (excess fuel), which can be caused by vacuum leaks or faulty EVAP components. I'm hoping to understand these issues so I can better prepare for a proper diagnosis and repair at a qualified mechanic. Any insights would be greatly appreciated. Thank you, Kate
The P0455 and P0172 codes are often related to EVAP system faults. A key diagnostic step is to block the evaporative emissions flow to the engine and monitor whether the P0172 code persists. If it remains, this suggests a faulty valve or solenoid in the EVAP system that isn't sealing properly—leading to an overly rich fuel mixture. The presence of P1451 (cannister vent solenoid issue) further supports this theory, as a failing vent solenoid can cause all three codes simultaneously. If I were working on this vehicle, I would prioritize checking the cannister vent solenoid and inspecting for vacuum leaks in the EVAP system before moving to more complex repairs.